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排序方式: 共有145条查询结果,搜索用时 234 毫秒
1.
Mirjana Stojanović 《BIT Numerical Mathematics》1990,30(1):171-176
It is proved that a spline difference scheme for a singularly perturbed self-adjoint problem, derived by using exponential cubic splines at mid-points, has second order uniform convergence in a small parameter . Numerical experiments are presented to confirm the theoretical predictions. 相似文献
2.
Inspired by the concept of multivalency and in pursuit of ever more intricate artificial molecular machines, we investigated the strict self-assembly of a triply threaded two-component superbundle, starting from a tritopic receptor in which three benzo[24]crown-8 macrorings are fused onto a triphenylene core and a trifurcated trication wherein three bipyridinium units are linked 1,3,5 to a central benzenoid core. The result of the investigation was quite unexpected and surprising. It transpired that the rapid formation of a doubly threaded two-component complex was followed by an extremely slow conversion (a week at 253 K in CD3COCD3 to reach equilibrium) of this kinetically controlled product into a thermodynamically controlled one, namely a triply threaded two-component superbundle. This intriguing observation begs the question: are there instances in nature where multivalency is expressed as a kinetically controlled process, prior to an equilibrium state being reached, and if so, what are the biological implications, if any? 相似文献
3.
Push-pull 2-alkylidene-4-oxothiazolidine vinyl bromides undergo efficient C(5) functionalization through DMSO-assisted carbon-bromine cleavage, followed by a bromine transfer-substitution (or elimination) sequence. A mechanism for this novel transformation is proposed. 相似文献
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6.
Dušica B. Stojanović Milorad Zrilić Radmila Jančić‐Heinemann Irena Živković Aleksandar Kojović Petar S. Uskoković Radoslav Aleksić 《先进技术聚合物》2013,24(8):772-776
New forms of hybrid multiaxial nanocomposites with enhanced mechanical and stab resisting properties are presented. This study is motivated by the lack of knowledge in the study of the multiaxial fabric nanocomposites with two modified thermoplastic matrices for antiballistic protection. Introduction of 5 wt.% silica nanoparticles in the composite of polyurethane/p‐aramid/poly (vinyl butyral) leads to significant improvement in mechanical properties, and the addition of silane as a coupling agents and glutaraldehyde as a crosslinking agents yielded maximal values of storage modulus, tensile modulus and anti‐stabbing properties for hybrid nanocomposites. Ballistic resistance testing and penetration depth of the hybrid nanocomposites were visualized using image analysis. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
7.
M. M. Vijatović Petrović J. D. Bobić H. Uršič J. Banys B. D. Stojanović 《Journal of Sol-Gel Science and Technology》2013,67(2):267-272
Barium titanate ceramics were prepared using the nanopowder resulting from a polymeric precursor method, a type of modified Pechini process. The obtained nanopowder was observed to agglomerate and in order to de-agglomerate the powder and enhance the properties of the barium titanate the material was attrition milled. The impact of this attrition milling on the electrical properties of the barium titanate was analysed. The temperature dependence of the relative dielectric permittivity showed three structural phase transitions that are characteristic for ferroelectric barium titanate ceramics. The relative dielectric permittivity at the Curie temperature was higher for the attrition-treated sample than for the non-treated barium titanate. The dielectric losses were below 0.04 in both barium titanate ceramics. The grain and grain-boundary contributions to the total resistivity were observed using impedance analyses for both ceramics. A well-defined ferroelectric hysteresis loop and piezoelectric coefficient d33 = 150 pC/N were obtained for the ceramics prepared from the de-agglomerated powder. In this way we were able to demonstrate that by attrition milling of chemically obtained powders the ferroelectric and piezoelectric properties of the ceramics could be enhanced. 相似文献
8.
Michael G. Sommer Petra Kureljak Dr. Damijana Urankar Dr. David Schweinfurth Nikolina Stojanović Dr. Martina Bubrin Dr. Martin Gazvoda Dr. Maja Osmak Prof. Dr. Biprajit Sarkar Prof. Dr. Janez Košmrlj 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(52):17296-17299
Azocarboxamide (azcH) has been combined for the first time with [Ru–Cym] to generate metal complexes with N,N‐ and N,O‐coordination mode, [(Cym)Ru(azc)Cl] and [(Cym)Ru(azcH)Cl]+[PF6]?. Geometric and electronic structures of the complexes are reported along with their in vitro activities against different tumour cell lines and preliminary results on solution chemistry. Compound [(Cym)Ru(azc)Cl] exhibited remarkable cytotoxic properties. It was cell‐type specific and had comparable IC50 values towards both cancer cells and their drug‐resistant subline. A tenfold increase in the sensitivity towards [(Cym)Ru(azc)Cl] was noted for the tumour cells with depleted intracellular glutathione (GSH) level, suggesting the essential role of GSH in cell response to this compound. 相似文献
9.
In this paper, the inhibition effect of silicate on emission or absorption of calcium was used for an investigation of the mechanism of formation of calcium silicate compounds. For that purpose, calcium chloride solutions were continuously titrated with a standard solution of sodium silicate (Na2SiO3), with simultaneous aspiration of the titrand into an air-hydrogen flame. During the titration, changes in the emission of the CaO-band at 622 nm and the CaOH-band at 554 nm were registered automatically on the recorder. Changes in the absorption of calcium were also registered at 422 nm. Thus curves of the same shape were obtained, with the same number of characteristic points, in which the SiO2/Ca ratio is constant, when the concentration of silicate in the titrant varies. This fact suggests that calcium reacts with silicate to form compounds with a constant composition.Curves of the same shape were obtained by titration of a standard solution of sodium silicate, with a calcium chloride solution, while monitoring the changes in the absorption of calcium at 422 nm and changes in the emission of the CaO-band at 622 nm. In this case, the mole ratios SiO2/Ca at the characteristic points of the curves were the same as in the case of the titration of calcium chloride solution with the silicate solution.On the basis of the mole ratios SiO2/Ca at the characteristic points on the titration curves, which amount to 0.21, 0.33 and 0.50, the mechanism of formation of calcium silicate compounds was represented by chemical equations.It may be concluded that in the process of evaporation of spray droplets a chain of reactions take place, resulting in compounds that can be represented by the general formula xCaO·SiO2. 相似文献
10.
Rade Markovi? Marija Baranac Zdravko D?ambaskiMilovan Stojanovi? Peter J Steel 《Tetrahedron》2003,59(39):7803-7810
Base-catalyzed reactions of β-oxonitriles 1 with diethyl mercaptosuccinate favour heterocyclization to afford 2-alkylidene-4-oxothiazolidines 3, rather than 2-alkylidene-4-oxo-1,3-thiazinanes 4. The observed regioselectivity is based on spectroscopic and experimental evidence, including a single-crystal X-ray structure determination. 相似文献